Automatic frequency control (AFC) is employed in two-way radio transceivers to compensate for any difference in frequency between the received signal frequency and the transceiver operating frequency. As is well known, AFC can be used for automatically compensating for frequency drifts in frequency generation devices or oscillators in radio transceivers due to aging, temperature fluctuations, and other effects. Thus, in both analog and digital communication, AFC is used in the radio transceiver to reduce and/or eliminate received and transmitted signal degradation and distortion due to the presence of this frequency difference.
Particularly in a microcontroller controlled radio transceiver, the microcontroller is used to control operation of AFC. Typically, the AFC is not operated in its most efficient manner since there are many factors to be considered in its implementation. For example, both the radio's operating environment and mode of transmission are important. Should the radio be operated in a portion of crowded radio spectrum or with transmission modes having a wide bandwidth, this may interface with the radio transceiver's capability to be on the proper frequency to receive or transmit information or data. Even in a transceiver utilizing a relatively narrow bandwidth such as digital frequency modulation (FM), AFC control will be required assuming that any frequency offset is larger than the oscillator step size and distortion due to AFC is not a factor. Moreover since there may be undesired signals in the frequency band of operation, the transceiver may inadvertently be tuned to these signals when in fact no tuning was necessary. Also, multiple spurious signals are often present, where the AFC may move the transceiver operating frequency to a great extent from the desired operating. If many undesired signals exist, the transceiver can be moved outside operating range.
Thus, the need exists to provide a system and method used with a microcontroller in a radio receiver or transceiver, for selecting the proper amount of AFC tuning compensation during varying signal conditions. This technique will ultimately prevent signal degradation and/or distortion due to improper tuning using AFC in the radio transceiver.